Curse of Vitality

The triggered ability of these Curses won’t trigger if only a planeswalker controlled by the enchanted player is attacked.

If you enchant yourself with one of these Curses, you’ll get its effects whenever another player attacks you.

A player is attacking another player if they control a creature that’s attacking that player. If no creatures are attacking the enchanted player as a Curse’s ability resolves (most likely because they’ve left the battlefield), only the Curse’s controller performs its actions.